The invention is generally directed to toner and developer compositions, and more specifically, the present invention is directed to developer and toner compositions containing charge enhancing additives, which impart or assist in imparting a negative charge to the toner particles and enable toners with rapid triboelectric charging characteristics. In one embodiment, there are provided in accordance with the present invention toner compositions comprised of resin, pigment particles and certain charge enhancing additives. In embodiments, the present invention is directed to toners with boric acid, the salts thereof, such as the alkali salts or mixtures thereof, charge enhancing additives and which toners exhibit improved characteristics. The aforementioned charge additives in embodiments of the present invention enable, for example, toners with rapid triboelectric charging characteristics, extended developer life, stable triboelectrical properties irrespective of changes in environmental conditions, such as relative humidity, and high image print quality with substantially no background deposits. The aforementioned toner compositions usually contain a colorant component comprised of, for example, carbon black, magnetites, or mixtures thereof, color pigments or dyes with cyan, magenta, yellow, blue, green, red, brown, or mixtures thereof thereby providing for the development and generation of black and/or colored images. The toner and developer compositions of the present invention can be selected for electrophotographic, especially xerographic, imaging and printing processes, including color processes.
Toners with negative charge additives are known, reference for example U.S. Pat. Nos. 4,411,974 and 4,206,064, the disclosures of which are totally incorporated herein by reference. The '974 patent discloses negatively charged toner compositions comprised of resins, pigment particles, and as a charge enhancing additive ortho-halophenyl carboxylic acids. Similarly, there are disclosed in the '064 patent toner compositions with certain chromium, cobalt, and nickel complexes as negative charge enhancing additives. In U.S. Pat. No. 4,845,003 there are illustrated negatively charged toners with certain aluminum salt charge additives. More specifically, this patent discloses as charge additives aluminum complexes comprised of two or three hydroxybenzoic acid ligands bonded to a central aluminum ion. While these charge additives may have the capability of imparting negative triboelectric charge to toner particles, they are generally not efficient in promoting the rate of triboelectric charging of toner particles. A fast rate of triboelectric charging is particularly crucial for high speed xerographic machines since, for example, these machines consume toner rapidly, and fresh toner has to be constantly added. The added uncharged toners, therefore, must charge up to their equilibrium triboelectric charge level rapidly to ensure no interruption in the xerographic imaging or printing operation. Another disadvantage with these charge additives is their thermal instability, that is they often break down during the thermal extrusion process of the toner manufacturing cycle. Most or many of these and other disadvantages are eliminated, or substantially eliminated with the toners containing the charge additives of the present invention.
Also of interest are U.S. Pat. Nos. 4,404,271; 4,656,112; 4,762,763; 4,845,003; 4,767,688; 4,378,420 and 4,433,040. Two of the charge additives of the aforementioned prior art, namely 1:2 boron 3,5-di-tertiarybutylsalicylic acid complex (LR 120.TM.), or 1:2 boron 3,5-dibutylsalicylic acid complex, when added to toner compositions have, it is believed, inferior characteristics, such as tribocharging characteristics, as compared to the toners of the present invention.
Developer compositions with charge enhancing additives, which impart a positive charge to the toner particles, are known. Thus, for example, there is described in U.S. Pat. No. 3,893,935 the use of quaternary ammonium salts as charge control agents for electrostatic toner compositions; U.S. Pat. No. 4,221,856 which discloses electrophotographic toners containing resin compatible quaternary ammonium compounds in which at least two R radicals are hydrocarbons having from 8 to about 22 carbon atoms, and each other R is a hydrogen or hydrocarbon radical with from 1 to about 8 carbon atoms, and A is an anion, for example sulfate, sulfonate, nitrate, borate, chlorate, and the halogens such as iodide, chloride and bromide, reference the Abstract of the Disclosure and column 3; a similar teaching is presented in U.S. Pat. No. 4,312,933 which is a division of U.S. Pat. No. 4,291,111; similar teachings are presented in U.S. Pat. No. 4,291,112 wherein A is an anion including, for example, sulfate, sulfonate, nitrate, borate, chlorate, and the halogens; U.S. Pat. No. 4,338,390, the disclosure of which is totally incorporated herein by reference, discloses developer compositions containing as charge enhancing additives organic sulfate and sulfonates, which additives can impart a positive charge to the toner composition; and U.S. Pat. No. 4,298,672, the disclosure of which is totally incorporated herein by reference, discloses positively charged toner compositions with resins and pigment particles, and as charge enhancing additives alkyl pyridinium compounds.
Illustrated in U.S. Pat. No. 5,275,900 are toner compositions comprised of polymer resins, colorants comprised of color pigment particles or dye molecules, and certain metal complex charge additives derived from the reaction of a mixture of a hydroxybenzoic acid and a base with a metal ion in the presence of an excess of a hydroxyphenol. More specifically, the copending application illustrates a negatively charged toner composition comprised of polymer, colorant, optional surface additives, and a metal complex charge enhancing additive of the following formula ##STR1## where M is a metal; N+ is a cation; R and R' are alkyl, alkoxy, aryloxy, halogen, carbonyl, amino, nitro, or mixtures thereof; m and n are the number of R substituents ranging from 0 to 3; y- is the magnitude of the negative charge of the anion; and y' represents the number of cations.
Illustrated in U.S. Pat. No. 5,300,387 is a negatively charged toner composition comprised of a polymer or polymers, pigment, and a metal complex charge enhancing additive as essentially represented by the following formula ##STR2## where M is the central metal ion; N+ is the counter cation; R and R' are selected from the group consisting of alkyl, alkoxy, aryloxy, halogen, carbonyl group, alkoxycarbonyl group, amino group, nitro group or mixtures thereof; m and n are the number of R substituents on the aromatic rings, ranging from 0 to 3; y- is the magnitude of the negative charge of the anion or the number of the counter cations of the metal complex, and represents the number 1 or 2; and y' represents the number of counter cations N+; U.S. Ser. No. 964,544 (D/92402) is a toner composition comprised of a polymer or polymers, pigment particles and/or dyes, optional surface additives, and a charge enhancing additive of the following formula ##STR3## wherein R is hydrogen, alkyl, or aryl; R' and R" are selected from the group consisting of alkyl, alkoxy, aryl, and aryloxy; R'" is selected from the group consisting of alkyl, alkoxy, oxide, and halide; M is boron or a metal; x is a number of from 1 to 4; and y is a number of from 0 to 2; and U.S. Pat. No. 5,290,651 is a negatively charged toner composition comprised of polymer, pigment, optional surface additives, and a zinc complex charge enhancing additive represented by either of the two following formulas ##STR4## wherein R, R', R", and R'" are independently selected from the group consisting of hydrogen, alkyl, aryl alkoxy, aryloxy, halogen, amino, and hydroxy. The disclosures of each of the aforementioned copending applications are totally incorporated herein by reference.
Illustrated in U.S. Pat. No. 5,256,515, the disclosure of which is totally incorporated herein by reference is a negatively charged toner composition comprised of resin particles, pigment particles, optional surface additives, and a halogenated salicylic acid complex charge enhancing additive of the following formula: ##STR5## wherein Z is zinc of chromium; M is hydrogen, an alkali metal, an alkaline earth metal, NH.sub.4, or NR.sub.4 wherein R is alkyl; X and Y are independently selected from the group consisting of chloride, iodide and bromide; and n and m are the numbers 1 or 2; and U.S. Pat. No. 5,256,514, the disclosure of which is totally incorporated herein by reference, there is illustrated a negatively charged toner composition comprised of resin particles, pigment particles, optional surface additives, and a halogenated salicylic acid charge enhancing additive of the following formula ##STR6## wherein X is halogen; M is hydrogen, an alkaline earth, an alkali metal or NR.sub.4 wherein R is alkyl; and n is the number 1 or 2.
While many charge enhancing additives are known, there continues to be a need for charge enhancing additives which, when incorporated in toners, render the toners with many of the advantages illustrated herein. There is also a need for economical negative charge enhancing additives which are useful for incorporation into black and colored toner compositions which can be utilized for developing positively charged electrostatic latent images. Moreover, there is a need for colored toner compositions containing charge enhancing additives which do not interfere with the color quality of the colorants present in the toners. Another need relates to the provision of toner compositions with certain charge enhancing additives, which toners in embodiments thereof possess substantially stable triboelectric charge levels, and display acceptable rates of triboelectric charging characteristics. Furthermore, there is also a need for toner compositions with certain charge enhancing additives which possess excellent dispersibility characteristics in toner resins, and can, therefore, form stable dispersions in the toner compositions. There is also a need for negatively charged black and colored toner compositions that are useful for incorporation into various imaging processes, inclusive of color xerography, as illustrated in U.S. Pat. No. 4,078,929, the disclosure of which is totally incorporated herein by reference; laser printers; and additionally a need for toner compositions useful in imaging apparatuses having incorporated therein layered photoresponsive imaging members, such as the members illustrated in U.S. Pat. No. 4,265,990, the disclosure of which is totally incorporated herein by reference. Also, there is a need for negatively charged toner compositions which have desirable triboelectric charge levels of, for example, from between about -10 to about -50 microcoulombs per gram, and preferably from about -10 to about - 30 microcoulombs per gram, and triboelectric charging rates of less than about 120 seconds as measured by standard charge spectrograph methods when the toners are frictionally charged against suitable carrier particles via conventional roll milling techniques. There is also a need for nontoxic, substantially nontoxic, or environmentally compatible charge enhancing additives which when incorporated at effective concentrations of, for example, less than 7 weight percent, and preferably less than 4 weight percent in toners, render environmentally acceptable toners. The concentrations of the charge additives that can be present generally range from about 0.05 weight percent to about 5 weight percent, depending on whether the charge additive is utilized as a surface additive or as a dispersion in the bulk of the toner. The effective concentrations of toner in the developer, that is toner and carrier particles, are, for example, from about 0.5 to about 5 weight percent, and preferably from about 1 to about 3 weight percent.